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  • Small system solar/battery

    I need a small solar/battery system to run a load 24/7. The load will draw about 26 AH/day @ 12V. I need at least 3 days of battery back up, 6-7 would be better. The site does get shade after about noon or 1pm but has decent morning sun. There might be some intermittent shading in the morning. I do not need an inverter. Lowest winter temp is around 0 F, highest summer temp is around 95 F. Normal winter lows are 20's and 30's, normal summer highs are 70's and 80's. We can get snow but it will usually melt off in 2-3 days, and except for when there is snow present I have access to the site. The site is at Lat 35 near Asheville NC.

    My thoughts:
    3 100 W panels in parallel in case one or two panels are in shade.
    Victron 100/20 MPPT charge controller - supposed to have excellent response for quickly changing shade/sun conditions + has bluetooth app.
    2 100-110 AH AGM deep cycle SLA batteries (should give 6+ days of back up)

    Questions:
    1) would a single 300+ watt panel be better than 3 separate panels, considering the possible shade?
    2) would the panels in series or parallel be better considering the possible shade.
    3) is there a solar panel manufacturer that would be better - the sweet spot in the solar industry is > 300 Watt panels so harder to find the lower wattage panels.
    4) might it be better to use 4 80 W panels in 2S2P configuration?
    5) What batteries are good for this? I was going to use Universal Power Group UB121000 or UB121100. I don't want to use LiFePo - too costly.
    6) where do I need circuit breakers and what size? I'd think 20 A between the PV and CC, 20A between CC and batteries and 2-3 A between the CC to the load.
    7) Lightning protection and where does it go?
    8) do I need a combiner box for the panels?
    9) 12v or 24V system - the load can take 12-28VDC
    10) is there an issue with equalization of the batteries, since the load is small compared to the available AH's? The Midnite Classic Controllers have an option to charge batteries every other or 3rd day.
    11) what am I missing?

    Thanks.

  • #2
    1) forget about haveing any panels in shade or any portion shaded

    2) MPPT controller on parallel 100w panels is no benefit, just use a PWM controller

    3) i'd suggest 2 golf cart batteries in series, to provide 12V @ 200ah A 300W 'grid tie" panel and a MPPT controller. Maybe add a 2nd panel in parallel if you think conditions are poor and you need more harvest on the rare sunny day
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

    Comment


    • #3
      Mike gave you a workable solution, but I will approach it a bit differently and give you some options.

      The load will draw about 26 AH/day @ 12V. I need at least 3 days of battery back up, 6-7 would be better.
      This demands two different solutions. For 3 days you need 6 day reserve capacity, and for 6 to 7 days requires 12 to 14 day capacity. Here is the catch, batteries need a C/10 to C/8 charge current. So be careful what you ask for because things get expensive.

      So for 3 day run time would require 26 AH x 6 = 156 AH lets just call it 150 AH. for 6-day would be 300 AH. That right there is some serious pocket change.

      For charging I disagree with Mike because MPPT wil be less expensive for either system. For a 150 AH battery will require 15 amp charge current. For that I would use a Morningstar SunSaver MPPT controller with a 200 watt Grid Tied Panel. About $400. You could use 12 volt 100 watt battery panels with MPPT, but to get 15 amps would require 300 watts of panel all wired in parallel with a combiner and fuses. That route would cost you more than $500 by going with an inexpensive PWM Controller.

      6-day reserve doubles the cost needing 2 x 200 watt Grid Tied Panels and a 30 amp MPPT Controller. That will cost you $700 to $800. You would not even want to consider using 12 volt battery panels and PWM as now you are talking 600 watts and a 30 amp PWM controller costing you $1100 or more and a lot of wire and fuses to wire 6 panels in parallel. Not even sure you can buy a combiner for 6 panels. Only a fool would do that.
      MSEE, PE

      Comment


      • #4
        Thanks for the info: Here's what I'm planning now, based on your comments. Does this make sense?

        1) Astronergy 280 W panel or Solarworld 285 W panel
        2) Victron 100/20 MPPT controller (want the bluetooth - system will be on top of water tank and want to avoid climbing)
        3 2 x 110 AH AGM SLA deep cycle Batteries

        The larger panel feeds into the larger CC which charges the larger batteries. These batteries should give me 4+ days of back up.

        The controller and panel will run about $310. Batteries will run around $400, misc parts (breakers, surge, enclosure, panel mount) around $500 for a total about $1100.

        Additional parts:
        1 10 A circuit breaker between panel and CC (max panel amps is under 10 A)
        2 20 A circuit breaker between CC and Batteries (CC only puts out 20A)
        3 3 A circuit breaker between CC and load (load is a bit over 1 A)
        4 Midnite 115V surge suppressor (connect between panel + and ground, every thing else will be inside a metal enclosure so shouldn't need a suppressor)

        Thanks again.

        Comment


        • #5
          Originally posted by billvolz View Post
          3 2 x 110 AH AGM SLA deep cycle Batteries
          You never ever want to parallel batteries unless it is necessary to obtain the AH capacity. Battery AH capacity upper limit is 6000 AH and you are no where close to that. So instead of using 2 x 12-volt 110 AH batteries in parallel, use 2 x 6-volt 220 AH batteries which are Golf Cart Batteries available in both FLA and AGM. Wire them in series and you got 12 volts at 220 AH.
          MSEE, PE

          Comment


          • #6
            Thanks Sunking. I will use 2 x Vmax 6v 225 AH batteries in series. They cost a bit more, but look to be better batteries than the ones I was going to use.


            Bill

            Comment


            • #7
              One more question - I plan to put the batteries in an Ameresco VL-BB-2 enclosure, along with the CC, circuit breakers and other stuff. As these are sealed batteries I assume that this practice is OK. If they were flooding acid batteries, I'd put them in a separate vented enclosure. This system will be located on top a remote water tank that I don't want to climb and also need minimum maintenance. Big mistake or not?

              Comment


              • #8
                "sealed" batteries still have over pressure vents, and at end of life of sealed batteries, they can vent.
                Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                solar: http://tinyurl.com/LMR-Solar
                gen: http://tinyurl.com/LMR-Lister

                Comment


                • #9
                  Thanks Mike. I have separate boxes for the two batteries and the other parts. And it's cheaper too. The enclosure for the other parts is 12x12x6 and I think is large enough for the CC, circuit breakers,a couple of surge suppressors and POE injector though I'm a bit concerned about space for running wires. For a few more bucks I can get a 12x14x6.

                  Comment


                  • #10
                    I really really like these fuses.
                    https://www.bluesea.com/products/215...k_-_30_to_300A
                    the mount right at the battery where they belong, you can get fuses most supply houses, and they have decent voltage rating on the fuse. It reduces the splice count in the heavy power cables. I like one fuse for inverter load and other for charge controller
                    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                    solar: http://tinyurl.com/LMR-Solar
                    gen: http://tinyurl.com/LMR-Lister

                    Comment

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